Chapter 10: Classes and Data Abstraction Objectives In this chapter, you will: – Learn about classes – Learn about private, protected, and public members of a class – Explore how classes are implemented – Become aware of accessor and mutator functions – Examine constructors and destructors C++ Programming: Program Design Including Data Structures, Seventh Edition Objectives (cont’d.) – Learn about the abstract data type (ADT) – Explore how classes are used to implement ADTs – Become aware of the differences between a struct and a class – Learn about information hiding – Explore how information hiding is implemented in C++ – Learn about the static members of a class C++ Programming: Program Design Including Data Structures, Seventh Edition Classes • Object-oriented design (OOD): a problem solving methodology • Objects: components of a solution • Class: a collection of a fixed number of components • Member: a component of a class C++ Programming: Program Design Including Data Structures, Seventh Edition Classes (cont’d.) • Class definition: – Defines a data type; no memory is allocated – Don’t forget the semicolon after the closing brace • Syntax: C++ Programming: Program Design Including Data Structures, Seventh Edition Classes (cont’d.) • Class member can be a variable or a function • If a member of a class is a variable – It is declared like any other variable – You cannot initialize a variable when you declare it • If a member of a class is a function – Function prototype is listed – Function members can (directly) access any member of the class C++ Programming: Program Design Including Data Structures, Seventh Edition Classes (cont’d.) • Three categories of class members: – private (default) • Member cannot be accessed outside the class – public • Member is accessible outside the class – protected C++ Programming: Program Design Including Data Structures, Seventh Edition Unified Modeling Language Class Diagrams • Unified Modeling Language (UML) notation: used to graphically describe a class and its members – +: member is public – -: member is private – #: member is protected C++ Programming: Program Design Including Data Structures, Seventh Edition Unified Modeling Language Class Diagrams (cont’d.) C++ Programming: Program Design Including Data Structures, Seventh Edition Variable (Object) Declaration • Once defined, you can declare variables of that class type clockType myClock; • A class variable is called a class object or class instance C++ Programming: Program Design Including Data Structures, Seventh Edition 10 In-line initialization of Data Members and the Default Constructor • C++11 standard allows member initialization in class declarations • Called in-line initialization • Can eliminate the need for a default constructor • Not all compilers recognize this feature C++ Programming: Program Design Including Data Structures, Seventh Edition 32 Arrays of Class Objects (Variables) and Constructors • If you declare an array of class objects, the class should have the default constructor C++ Programming: Program Design Including Data Structures, Seventh Edition 33 Destructors • Destructors are functions without any type • The name of a destructor is the character '~' followed by class name – For example: ~clockType(); • A class can have only one destructor – The destructor has no parameters • Destructor automatically executes when the class object goes out of scope C++ Programming: Program Design Including Data Structures, Seventh Edition 34 Data Abstract, Classes, and Abstract Data Types • Abstraction – Separating design details from usage – Separating the logical properties from the implementation details • Abstraction can also be applied to data • Abstract data type (ADT): data type that separates the logical properties from the implementation details C++ Programming: Program Design Including Data Structures, Seventh Edition 35 A struct Versus a class • By default, members of a struct are public – private specifier can be used in a struct to make a member private • By default, the members of a class are private • classes and structs have the same capabilities C++ Programming: Program Design Including Data Structures, Seventh Edition 36 A struct Versus a class (cont’d.) • In C++, the definition of a struct was expanded to include member functions, constructors, and destructors • If all member variables of a class are public and there are no member functions – Use a struct C++ Programming: Program Design Including Data Structures, Seventh Edition 37 Information Hiding • Information hiding: hiding the details of the operations on the data • Interface (header) file: contains the specification details • File extension is h • Implementation file: contains the implementation details • File extension is cpp • In header file, include function prototypes and comments that briefly describe the functions – Specify preconditions and/or postconditions C++ Programming: Program Design Including Data Structures, Seventh Edition 38 Information Hiding (cont’d.) • Implementation file must include header file via include statement • In include statement: – User-defined header files are enclosed in double quotes – System-provided header files are enclosed between angular brackets C++ Programming: Program Design Including Data Structures, Seventh Edition 39 Information Hiding (cont'd.) • Precondition: A statement specifying the condition(s) that must be true before the function is called • Postcondition: A statement specifying what is true after the function call is completed C++ Programming: Program Design Including Data Structures, Seventh Edition 40 Executable Code • To use an object in a program – The program must be able to access the implementation • Visual C++ 2015 Express, Visual Studio 2015, and C++ Builder put the editor, compiler, and linker into a package – One command (build, rebuild, or make) compiles program and links it with the other necessary files – These systems also manage multiple file programs in the form of a project C++ Programming: Program Design Including Data Structures, Seventh Edition 41 Static Members of a Class • Use the keyword static to declare a function or variable of a class as static • A public static function or member of a class can be accessed using the class name and the scope resolution operator • static member variables of a class exist even if no object of that class type exists C++ Programming: Program Design Including Data Structures, Seventh Edition 42 Static Members of a Class (cont’d.) • Multiple objects of a class each have their own copy of non-static member variables • All objects of a class share any static member of the class C++ Programming: Program Design Including Data Structures, Seventh Edition 43 Summary • Class: collection of a fixed number of components • Members: components of a class – Accessed by name – Classified into one of three categories: • private, protected, and public • Class variables are called class objects or, simply, objects C++ Programming: Program Design Including Data Structures, Seventh Edition 44 Summary (cont’d.) • The only built-in operations on classes are assignment and member selection • Constructors guarantee that data members are initialized when an object is declared – Default constructor has no parameters • Destructor automatically executes when a class object goes out of scope – A class can have only one destructor – The destructor has no parameters C++ Programming: Program Design Including Data Structures, Seventh Edition 45 Summary (cont’d.) • Abstract data type (ADT): data type that separates the logical properties from the implementation details • A public static member, function or data, of a class can be accessed using the class name and the scope resolution operator • Static data members of a class exist even when no object of the class type exists • Instance variables: non-static data members C++ Programming: Program Design Including Data Structures, Seventh Edition 46 ... protected C++ Programming: Program Design Including Data Structures, Seventh Edition Unified Modeling Language Class Diagrams (cont’d.) C++ Programming: Program Design Including Data Structures,... – Assignment (=) C++ Programming: Program Design Including Data Structures, Seventh Edition 12 Assignment Operator and Classes C++ Programming: Program Design Including Data Structures, Seventh... operator :: C++ Programming: Program Design Including Data Structures, Seventh Edition 19 Implementation of Member Functions (cont’d.) C++ Programming: Program Design Including Data Structures,